Strength is weakness on the Internet

Jul 26, 2000

The very feature of the Internet that makes it so robust against random connection
failures might leave it vulnerable to intelligent attack, according to Albert-Laszlo Barabasi and
co-workers in the physics department of the University of Notre Dame in Indiana (Nature406
378). The consequences of such deliberate sabotage would be enormous in a business world
that is becoming ever-more dependent on electronic communications.

In a 'scale-free' network of many interconnected nodes, like the Internet, most of the nodes
are connected to a relatively small number of other nodes. Only a very small minority have a
large number of connections. It is therefore extremely unlikely that randomly failing links
would have a catastrophic effect on the whole network. In contrast, an intelligent attack on the
few highly connected nodes could be devastating.

Barabasi and co-workers studied the effect that removing random nodes from a scale-free
network had on the ability of the remaining nodes to communicate with each other,
and the degree to which the network became fragmented. They found that the
network's performance remained constant, even after they had removed as many of
5% of the nodes, and that it was resistant to fragmentation. But when the team
simulated an intelligent attack by targeting the highly connected nodes, it was a
different story: the network became fragmented very quickly, and with 5% of the
nodes missing, its ability to communicate was halved.

The team applied tools and ideas from statistical mechanics to the Internet. "I believe that for
many complex systems, we have to first understand the topology that describes how the
diverse constituents interact with each other", Barabasi told PhysicsWeb. "This is
fundamentally a physics problem, since it involves randomness and self-organization living
side by side, and that is best addressed by the tools of statistical mechanics."

Error tolerance may come at the expense of reduced robustness in a scale-free network like
the Internet, but Barabasi and colleagues point out that this peculiar feature can be exploited
in scale-free systems such as metabolic networks, where drug design can target
vulnerable points. But it is not a promising development for the Internet.